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[nextpage title=”Introduction”]

ASUS is the number one motherboard manufacturer in the world and they’ve been expanding to other business for several years, recently reaching the power supply market. Though ASUS power supplies are not sold in the US, this didn’t prevent us from getting our hands on their 500 W product, which is sold throughout the world. Manufactured by Delta Electronics, does this power supply carry ASUS high-quality standards? Let’s see.

ASUS P-50GA 500 W power supplyFigure 1: ASUS P-50GA 500 W power supply.

ASUS P-50GA 500 W power supplyFigure 2: ASUS P-50GA 500 W power supply.

P-50GA is a short 5 ½” (140 mm) power supply, having a 120 mm fan on its bottom, active PFC and no modular cabling system.

All cables have a nylon protection, but the sleevings don’t come from inside the power supply, as you can see in Figure 2. The cables included on P-50GA are:

  • Main motherboard cable with a 20/24-pin connector.
  • One cable with one EPS12V connector and one ATX12V connector.
  • One cable with two six/eight-pin auxiliary power connectors for video cards.
  • Two SATA power cables with two plugs each.
  • One peripheral power cable with three standard peripheral power plugs and one floppy disk drive power connector.
  • One peripheral power cable with three standard peripheral power plugs.

The cables are somewhat short, having 17 21/64” (44 cm) between the power supply housing and the first connector on the cable and 5 ½” (140 mm) between connectors, on cables with more than one connector. The length of the cables may make it difficult for you to use this power supply inside a full tower case or even on a mid-tower case where the power supply is installed on the bottom of the case.

Almost all wires are 18 AWG. The ATX12V/EPS12V cable uses 20 AWG wires, which are thinner than we’d like to see on a 500 W product.

The number of connectors available is enough for you to build an entry-level or mainstream PC, but it would be nice to see at least six SATA power plugs. The two video card power connectors available are installed on the same cable, which isn’t the best configuration: it is always better to see them using individual cables.

ASUS P-50GA 500 W power supplyFigure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The P-50GA”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

ASUS P-50GA 500 W power supplyFigure 4: Overall look.

ASUS P-50GA 500 W power supplyFigure 5: Overall look.

ASUS P-50GA 500 W power supplyFigure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

This power supply has one X capacitor, one coil and two Y capacitors more than the minimum required plus two Y capacitors and one X capacitor after the rectification bridges, but it doesn’t come with a MOV, which is a sin. This component is in charge of surge protection. We expected it to have one, since it carries the name ASUS.

ASUS P-50GA 500 W power supplyFigure 7: Transient filtering stage (part 1).

ASUS P-50GA 500 W power supplyFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the ASUS P-50GA.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of ASUS P-50GA. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ8J rectifying bridges in its primary connected in parallel and attached to a heatsink. Each bridge can deliver up to 8 A at 100° C or 6 A at 45° C if a heatsink is used, which is the case. So this stage supports up to 16 A, so in theory, you would be able to pull up to 1,840 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,472 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

ASUS P-50GA 500 W power supplyFigure 9: Rectifying bridges.

Two SPW20N60C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference tempe
rature makes) or up to 62.1 A at 25° C in pulse mode. These transistors present a maximum resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Chinese from Samxon and rated at 85° C.

In the switching section, another two SPW20N60C3 power MOSFET transistors are used.

ASUS P-50GA 500 W power supplyFigure 10: Active PFC transistors and diode. The switching transistors are on the other side of the heatsink.

Instead of using one PFC/PWM combo chip, this power supply uses separated controllers. For controlling the active PFC circuit one UCC3818AN PFC controller is used, while for controlling the switching transistors one UC3845B PWM controller is used (this is a tiny component soldered on the solder side of the printed circuit board).

ASUS P-50GA 500 W power supplyFigure 11: PFC controller.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

ASUS P-50GA uses five Schottky rectifiers on the secondary, plus an LM7912 voltage regulator to regulate the -12 V output.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two STPS30H100CT (30 A, 15 A per internal diode at 155° C, 0.67 V voltage drop) Schottky rectifiers, giving us a maximum theoretical current of 43 A or 514 W for the +12 V output. Interesting enough the rectifier used on the direct rectification uses a TO-220 packaging (STPS30H100CT), while the rectifier used for the “freewheeling” part uses a TO-247 packaging (STPS30H100CW).

The +5 V output is produced by two STPS20L45CT Schottky rectifiers, which one capable of handling up to 20 A (10 A per internal diode at 135° C, maximum forward voltage of 0.5 V). This gives us a maximum theoretical current of 29 A or 143 W for the +5 V output.

The +3.3 V output is produced by one STPS3045CW Schottky rectifier (30 A, 15 A per internal diode at 155° C, 0.57 V voltage drop). This gives us a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

ASUS P-50GA 500 W power supplyFigure 12: -12 V voltage regulator and rectifiers.

Instead of using a monitoring integrated circuit this power supply implements a discrete solution, so we couldn’t check what protections this power supply really has. The small daughterboard located on the secondary is in charge of providing the protections, controlling the fan,  generating the power good signal and turning the power supply on and off.

ASUS P-50GA 500 W power supplyFigure 13: Secondary daughterboard.

Electrolytic capacitors from the secondary are all from Ltec and labeled at 105° C, as usual.

[nextpage title=”Power Distribution”]

In Figure 14, you can see the power supply label containing all the power specs.

ASUS P-50GA 500 W power supplyFigure 14: Power supply label.

This power supply has three rails, distributed like this:

  • +12V1 (solid yellow wire): Main motherboard, SATA and peripheral power connectors.
  • +12V2 (yellow wire with black stripe): ATX12V/EPS12V connectors.
  • +12V3 (solid yellow wire): Video card power connector.

This distribution is perfect, as it separates the CPU (ATX12V/EPS12V), the video card and all the rest on different rails.

Now let’s see if this power supply can really deliver 500 W.[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

The +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester and during all tests the +12V1 input was connected to the power supply +12V1 and +12V3 rails while the +12V2 input was connected to the power supply +12V2 rail.

< td>102.7 W

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 4 A (48 W) 7 A (84 W) 11 A (132 W) 14.5 A (174 W) 18 A (216 W)
+12V2 3 A (36 W) 7 A (84 W) 10 A (120 W) 14 A (168 W) 18 A (216 W)
+5V 1 A (5 W) 2 A (10 W) 4 A (20 W) 5 A (25 W) 6 A (30 W)
+3.3 V 1 A (3.3 W) 2 A (6.6 W) 4 A (13.2 W) 5 A (16.5 W) 6 A (19.8 W)
+5VSB 1 A (5 W) 1 A (5 W) 1.5 A (7.5 W) 2 A (10 W) 2.5 A (12.5 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 193.3 W 294.8 W 391.8 W 487.2 W
% Max Load 20.5% 38.7% 59.0% 78.4% 97.4%
Room Temp. 47.7° C 46.9° C 47.0° C 48.5° C 45.4° C
PSU Temp. 49.8° C 49.2° C 49.3° C 52.0° C 51.0° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 129.6 W 238.6 W 369.1 W 501.0 W 645.0 W
Efficiency 79.2% 81.0% 79.9% 78.2% 75.5%
AC Voltage 109.9 V 108.1 V 106.3 V 106.1 V 104.3 V
Power Factor 0.989 0.995 0.996 0.997 0.998
Final Result Pass Pass Pass Pass Pass

ASUS P-50GA can really deliver 500 W at 45° C. The problem is that wattage isn’t everything and P-50GA presents efficiency below 80% almost all times, and this explains why this power supply isn’t 80 Plus-certified.

Voltages were always inside the 5% tolerance set by ATX specification (10% for -12 V) and presented low noise and ripple levels. Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

ASUS P-50GA 500 W power supplyFigure 15: +12V1 input from load tester at 487.2 W (46.6 mV).

ASUS P-50GA 500 W power supplyFigure 16: +12V2 input from load tester at 487.2 W (46.8 mV).

ASUS P-50GA 500 W power supplyFigure 17: +5V rail with power supply delivering 487.2 W (12.8 mV).

ASUS P-50GA 500 W power supplyFigure 18: +3.3 V rail with power supply delivering 487.2 W (12.2 mV).

Let’s see if we could pull more than 500 W from the reviewed unit.

[nextpage title=”Overload Tests”]

As you know by now, before overloading a power supply we like to see if the over current protection is active and its trigger point. To test this we set current at +12V1 at 1 A and increased current on +12V2 until the power supply shut down. This happened when we tried to pull more than 20 A from the +12V2 rail. It was nice to see the OCP circuit configured at a value close to what is printed on the label (18 A).

Then starting from test five we increased current on all outputs until we reached the maximum the power supply could deliver still working inside ATX specs. The result you can see below. If we increased one amp on any output ripple was higher than the maximum allowed.

The main goal of our overload test is to see if the power supply burns or explodes and if its protections are active. Thus ASUS P-50GA passed this test.

We could pull up to 687 W from this unit, which is always good to see. The problem was efficiency, that was below 70% on this extreme configuration.

Input Maximum
+12V1 20 A (240 W)
+12V2 20 A (240 W)
+5V 22 A (110 W)
+3.3 V 22 A (72.6 W)
+5VSB 2.5 A (30 W)
-12 V 0.5 A (6 W)
Total 686.8 W
% Max Load 137.4%
Room Temp. 47.5° C
PSU Temp. 54.3° C
AC Power 988.0 W
Efficiency 69.5%
AC Voltage 99.1 V
Power Factor 0.998

[nextpage title=”Main Specifications”]

ASUS P-50GA power supply specs include:

  • ATX12V 2.2
  • Nominal labeled power: 500 W.
  • Measured maximum power: 686.8 W at 47.5° C.
  • Labeled efficiency: N/A
  • Measured efficiency: Between 75.5% and 81.0% at 115 V (nominal, see complete results for actual voltage).
  • Active PFC: Yes.
  • Modular Cabling System: No.
  • Motherboard Power Connectors: One 20/24-pin connector, one ATX12V connector and one EPS12V connector.
  • Video Card Power Connectors: Two six/eight-pin connectors.
  • SATA Power Connectors: Four in two cables.
  • Peripheral Power Connectors: Six in two cables.
  • Floppy Disk Drive Power Connectors: One.
  • Protections: Over current (tested and working), over voltage (OVP, not tested), under voltage (UVP, not tested), over power (OPP, not tested), over temperature (OTP), no load (NLO) and short-circuit (SCP, tested and working) protections.
  • Warranty: N/A.
  • More Information: https://www.asus.com
  • Average price in the US: We couldn’t find this product being sold in the USA.

[nextpage title=”Conclusions”]

We have one good and one bad news. The good news is that ASUS P-50GA can really deliver 500 W at 45° C. The bad news is that it presents low efficiency, below 80% almost all times, and this explains why this power supply isn’t 80 Plus-certified.

Even though it won’t burn or explode if you try to pull its labeled power – in fact we could pull up to 687 W from it (with a lousy 69.5% efficiency, however) – wattage isn’t everything. ASUS P-50GA will work fine, but we can’t recommend a power supply that can’t deliver at least 80% efficiency, since there are far better options on the market.

We are really disappointed by this power supply; we expected more from a product carrying the ASUS brand. This is the living proof that one company good at one segment may not be so got at another.